Traditionally, growers have used chemical pesticides as a means to control agronomically important pests. The introduction of transgenic plants carrying the delta-endotoxin from Bacillus thuringiensis (Bt) afforded a non-chemical method of control. Bt toxins have traditionally been categorized by their specific toxicity towards specific insect categories. For example, the Cry1 group of toxins are toxic to Lepidoptera The Cry1 group includes, but is not limited to, Cry1A(a), Cry1A(b) and Cry1A(c). See Hofte et al (1989) Microbiol Rev 53: 242–255.
Lepidopteran insects cause considerable damage to maize crops throughout North America and the world. One of the leading pests is Ostrinia nubilalis, commonly called the European corn borer (ECB). Genes encoding the crystal proteins Cry1A(b) and Cry1A(c) from Bt have been introduced into maize as a means of ECB control. These transgenic maize hybrids have been effective in control of ECB. However, developed resistance to Bt toxins presents a challenge in pest control. See McGaughey et al. (1998) Nature Biotechnology 16: 144–146; Estruch et al. (1997) Nature Biotechnology 15:137–141; Roush et al. (1997) Nature Biotechnology 15 816–817; and Hofte et al. (1989) Microbiol. Rev. 53: 242–255.
The primary site of action of Cry1 toxins is in the brush border membranes of the midgut epithelia of susceptible insect larvae such as lepidopteran insects. Cry1A toxin binding polypeptides have been characterized from a variety of Lepidopteran species. A Cry1A(c) binding polypeptide with homology to an aminopeptidase N has been reported from Manduca sexta, Lymantria dispar, Helicoverpa zea and Heliothis virescens. See Knight et al (1994) Mol Micro 11: 429–436; Lee et al. (1996) Appl Environ Micro 63: 2845–2849; Gill et al. (1995) J Biol. Chem 270: 27277–27282; and Garczynski et al. (1991) Appl Environ Microbiol 10: 2816–2820.
Another Bt toxin binding polypeptide (BTR1) cloned from M. sexta has homology to the cadherin polypeptide superfamily and binds Cry1A(a), Cry1A(b) and Cry1A(c). See Vadlamudi et al. (1995) J Biol Chem 270(10):5490–4, Keeton et al. (1998) Appl Environ Microbiol 64(6):2158–2165; Keeton et al. (1997) Appl Environ Microbiol 63(9):3419–3425 and U.S. Pat. No. 5,693,491.
A homologue of BTR1 that demonstrates binding to Cry1A(a) was isolated from Bombyx mori as described in Ihara et al. (1998) Comparative Biochemistry and Physiology, Part B 120:197–204 and Nagamatsu et al. (1998) Biosci. Biotechnol. Biochem. 62(4):727–734. In addition, a Bt-binding protein that is also a member of the cadherin superfamily was isolated from Heliothis virescens, the tobacco budworm (see Gahan et al. (2001) Science 293:857–860 and GenBank accession number AF367362).
Identification of the plant pest binding polypeptides for Bt toxins are useful for investigating Bt toxin-Bt toxin receptor interactions, selecting and designing improved toxins, developing novel insecticides, and new Bt toxin resistance management strategies.